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Histology > Immune System Lecture > Flashcards

Immune System Lecture Flashcards

1
Q

Lymphatic system

A

a group of cells, tissues, and organs that monitor body surfaces and fluid compartments

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2
Q

Immune system

A

organs and vessels of the lymphatic system linked together and connected to the vascular system that monitor and destroy foreign substances, pathogens, and neoplastic cells. Also provide a means to respond to previously encountered foreign materials

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3
Q

Organs of the immune system

A

Thymus
Bone marrow
Lymph nodes
Spleen

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4
Q

Thymus

A

–> site of maturation of immature T lymphocytes

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5
Q

Bone marrow

A

-> home of lymphocyte stem cells and site of B lymphocyte maturation

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6
Q

Lymph nodes

A

–> interact with antigen and antigen presenting cells from circulating
lymph and undergo activation and cell division

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7
Q

Spleen

A

–> where T and B lymphocytes may interact with blood-borne antigen

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8
Q

Primary lymphoid organs

A

locations where lymphocytes are trained to recognize and
destroy specific antigens

o Bone marrow
o Thymus
o Bursa of Fabricious

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9
Q

Secondary lymphoid organs

A

locations where lymphocytes are activated in response to antigens

o Mucosal-associated lymphatic tissue (MALT)
o Lymph nodes
o Lymph nodules
o Tonsils

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10
Q

Describe the site of origin and maturation of B cells and T cells

A

B lymphocytes
­ Generated from a stem cell in the bone marrow
­ Mature in the bone marrow
­ Reside in lymph nodes, lymph nodules

T lymphocytes
­ Produced from stem cell in bone marrow
­ Differentiated (mature) in the thymus

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11
Q

B cells function

A

functions as APC, produces Abs (humoral immunity). Genetically programmed to respond to a single antigen or antigenic site. They create a type of protein called an antibody. These antibodies bind to pathogens or to foreign substances, such as toxins, to neutralize them. For example, an antibody can bind to a virus, which prevents it from entering a normal cell and causing infection.

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12
Q

T cells functions

A

Function in cell-mediated immunity. T cells are a part of the immune system that focuses on specific foreign particles. Rather than generically attack any antigens, T cells circulate until they encounter their specific antigen. As such, T cells play a critical part in immunity to foreign substances.

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13
Q

Antigen

A

a substance that can induce an immune response

  • Antigens are any substances that the immune system can recognize and that can thus stimulate an immune response.
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14
Q

Epitope

A

small part of Ag that Abs bind to

  • An epitope is the part of an antigen that the host’s immune system recognizes, eliciting the immune response to an invading pathogen. It specifically binds to the corresponding antigen receptor on the immune cell (such as a B cell) and binding only occurs if the structures are complementary
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15
Q

Antibody

A

a protein that is specific for a particular substance (depends on shape and charge of the substance)

Antibodies are proteins that protect you when an unwanted substance enters your body. Produced by your immune system, antibodies bind to these unwanted substances in order to eliminate them from your system.

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16
Q

Cluster of differentiation

A

surface proteins that have been identified by a specific monoclonal Abs

  • The cluster of differentiation (CD) is a protocol used for the identification and investigation of cell surface molecules present on leukocytes. CD molecules often act as receptors or ligands important to the function of immune cells.
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17
Q

IgM

A
  • Produced early in immune response
  • Effective agglutinated
  • First produced in early embryonic life
  • Effective first line of defense against bacteria
  • 3rd most abundant serum Ab
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18
Q

IgD

A
  • Present on nearly all lymphocytes
  • 4th most abundant serum Ab
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19
Q

IgG

A
  • Most abundant serum Ab of internal body fluids especially extravascular, where it combats microorganism and their toxins
  • A good precipitating Ab
  • Binds to macrophages and neutrophils
  • Crosses the placenta
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20
Q

IgA

A
  • Major Ab of seromucous secretions, where it defends external body surfaces (e.g. saliva, tears, colostrum of milk)
  • Bind to macrophages and neutrophils
  • 2nd most abundant serum Ab
  • Endocytosed by epithelial cells and transported to apical surface for release into lumen
21
Q

IgE

A
  • Protect external body surfaces
  • Recruits antimicrobial agents
  • Elevated in parasitic infections
  • Central to atopic allergic reactions, and anaphylaxis
  • Bound to eosinophils and mast cells
  • 5th most abundant serum Ab
22
Q

Humoral (antibody-mediated) immunity

A

B cells and plasma cells produce Abs that act directly on invading agent (e.g.)

23
Q

Cell-mediated immunity

A

T cells attack and destroy virus-infected host cells, tumor cells, and foreign cells

24
Q

MHC

A

cell proteins that combine with Ag fragments to form proteins to form a unit that is presented on cell surface

25
Q

MHC 1

A
  • Found on surface of all nucleated cells
  • Presents Ag to cytotoxic T cells
26
Q

MHC 2

A
  • Found on surface of B cells, some macrophages, dendritic cells, Langerhans cells, and some activated T cells
  • Presents Ag to T helped cells
27
Q

B lymphocytes (B cells)

A
  • Generated from a stem cell in bone marrow
  • Mature in bone marrow
  • Reside in lymph nodes, lymph nodules
  • Functions as APC; produces Abs (humoral immunity)
  • MHC II
  • Genetically programmed to respond to a single antigen or antigenic site
  • Plasma cells –> activated B cells that secrete a specific Ab
  • Memory cells –> subset of activated B cells capable of responding to same Ag in the future
28
Q

Macrophages

A
  • a large phagocytic cell found in stationary form in the tissues or as a mobile white blood cell, especially at sites of infection.
  • Macrophages are effector cells of the innate immune system that phagocytose bacteria and secrete both pro-inflammatory and antimicrobial mediators. In addition, macrophages play an important role in eliminating diseased and damaged cells through their programmed cell death.
29
Q

Dendritic cells

A
  • are professional antigen-presenting cells that link innate and adaptive immunity and are critical for the induction of protective immune responses against pathogens.
30
Q

Epithelioreticular cells

A
  • cells of medulla express MHC (major histocompatibility complex) proteins and present “self Ags (antigens) to maturing T cells. Any T cell that reacts to “self antigens” are removed via apoptosis (clonal deletion) to prevent development of autoimmunity.
  • Besides the role of providing a structural support for lymphocytes, epithelial reticular cells are responsible for the secretion of thymic hormones which promote lymphocyte proliferation and maturation.
31
Q

Langerhans cells

A
  • Beside in the epidermis as a dense network of immune system sentinels. These cells determine the appropriate adaptive immune response (inflammation or tolerance) by interpreting the microenvironmental context in which they encounter foreign
32
Q

Kupffer cells

A
  • a phagocytic cell which forms the lining of the sinusoids of the liver and is involved in the breakdown of red blood cells.
  • Kupffer cells are resident liver macrophages and play a critical role in maintaining liver functions. Under physiological conditions, they are the first innate immune cells and protect the liver from bacterial infections
33
Q

Helper T (TH1)

A
  • Interacts with cytotoxic T lymphocytes, NK cells, and macrophages in cell-mediated responses
34
Q

Helper T (TH2)

A
  • Interacts with B cells
  • Essential for Ag-Ab immune responses that control extracellular pathogens
35
Q

T lymphocytes

A
  • Produced from stem cell in bone marrow
  • Differentiated (mature) in the thymus
  • Long lived
  • Function in cell-mediated immunity
36
Q

T cytotoxic

A
  • Kill virus infected cells, cancer cells, cells infected with microorganisms, parasites, and transformed cells
37
Q

Suppressor T lymphocytes

A
  • Suppresses immune responses of other cells and inhibit activities like T cell activation, B cell differentiation, RBC maturation in bone marrow
38
Q

Gamma/delta T lymphocytes

A
  • Migrate into various epithelial tissues and remain
  • First line of defense against invading organism
39
Q

Explain the structure and function of natural killer (NK) cells.

A
  • Large, granular lymphocytes
  • Arise from common lymphoid stem cell in bone marrow
  • Matures outside of thymus
  • Important in killing viruses and tumor cells; part of early host response before cytotoxic T cells are activated
  • Killing similar to T cytotoxic cells (release of granules)
  • No memory response

Natural killer (NK) cells are effector lymphocytes of the innate immune system that control several types of tumors and microbial infections by limiting their spread and subsequent tissue damage.

40
Q

Primary immune response

A
  1. Lymph containing Ags usually enters lymph node via afferent lymphatics (*lymphocytes can also enter via arterioles)
  2. Lymph flow: cortex –> para cortex –> medulla –> exits lymph node via efferent lymphatics at hilus
  3. Ag contacts macrophages in medulla; macrophages engulf Ag and break it down into small fragments; some fragments bind with intracellular proteins and form MHC that becomes attached to cell surface
  4. Macrophages move into the paracortex to interact with T cells capable of responding to specific Ag
  5. T cells migrate to cortex to interact with specific B cells, which stimulates their proliferation
  6. B cells migrate from cortex to medulla, and leave lymph node via efferent lymphatics
  • Get small amount of Abs
  • Takes about 10 days to get detectable Ab levels
  • Most important function of B cells –> find specific Ag it can bind with
  • Increase # of B cells (plasma cells – secrete Ab; memory cells) that can respond to a particular Ag upon future encounters
41
Q

Secondary immune response

A
  1. Specific Ag reintroduced to lymph node gets trapped by dendritic cells primarily in cortex and paracortex
  2. Presentation of Ag to T cells, then B cells
  3. Rapid expansion of memory B cells into plasma cells that secrete large amounts of circulating Ab; production of more memory cells
  • Large amount of circulating Abs produced
  • Takes 1-2 days for secondary response to occur after Ag reintroduction
  • Much for effective than primary response
42
Q

Describe the structure, location, and function of the thymus.

A
  • Primary lymphoid organ originating from the 3rd and 4th pharyngeal pouches
  • Flattened, located within the mediastinum and neck (juveniles)
  • Largest and most active at birth; regresses (involutes) with age
    o Cortex
     Densely populated with immature lymphoblasts
     Mitotic replication and maturing T cells during movement to medulla
    o Medulla
     Sparsely populated with thrombocytes
     Thymic (Hassall’s) corpuscles
    The thymus is an organ that is critically important to the immune system which serves as the body’s defense mechanism providing surveillance and protection against diverse pathogens, tumors, antigens and mediators of tissue damage
43
Q

Explain how developing T cells are processed in the thymus.

A

– Cortex
1. Developing T cells express CD4 and CD8
2. Epithelioreticular cells present self MHC with self and foreign Ags to developing T cells
3. Positive response of T cells to self-MHC and self or foreign Ags = survival (positive selection); negative response to any presentations = death of T cell
4. Migration to medulla
– Medulla
5. Epithelioreticular cells present MHC and self Ag to T cells
* 6. Positive T cell response (recognition of self-MHC + Self Ags) = death of T cell; negative response = survive (negative selection)
* 7. Cells programmed as either T helper (CD4+) or T cytotoxic (CD8+) cells

44
Q

Explain the pattern of movement of T cells in and out of the thymus.

A
  • Blood supply
    – Thymic arteries pass through interlobular connective tissue and enter parenchyma at corticomedullary junction of lobules
    – split into cortical and medullary arterioles and capillaries (no cells move in or out of cortical blood vessels)
    – Post capillary venules (    permeable; allows movement of immature T cells in, and mature T cells out) located in medulla near corticomedullary junction
  • Epithelioreticular cells of medulla express MHC (major histocompatibility complex) proteins and present “self Ags (antigens) to maturing T cells. Any T cell that reacts to “self antigens” are removed via apoptosis (clonal deletion) to prevent development of autoimmunity.
45
Q

Describe the structure, location, and function of the spleen.

A
  • Function
    – Filters blood
    – Removes old, worn-out blood cells
    – Recycles bilirubin and iron from red blood cells (RBCs)
    – Cell-mediated (T-cells) and humoral antibody (B-cells) responses
    – Phagocytosis of bacteria, protozoa, and RBC parasites
    – Storage of blood and platelets (*storage of up to ⅓ of all circulating platelets)
  • Structure
    – Fibroelastic capsule containing smooth muscle fused with overlying peritoneum
    – Trabeculae extend from capsule into organ creating incomplete subdivisions
    – Reticular fibers make up large proportion of stroma
    – No cortex or medulla
    – Scattered nodules (red pulp, white pulp)
    – White pulp
  • Splenic nodules (Malpighian corpuscles)
  • Concentration of B cells
  • Usually contain germinal centers (proliferation of B cells after activation)
    – Red pulp
  • Tissue between splenic corpuscles and trabeculae
  • Highly vascular
46
Q

Explain the structure, location, and function of lymph nodes.

A
  • Dense, encapsulated, bean or spherical shaped organs
  • Consistently found in specific regions of the body as clusters called lymphocenters
  • Filter lymph to search for foreign antigens, pathogens and tumor cells
  • Respond to antigenic stimulation by enlarging through clonal expansion of B-cells
47
Q

Describe the route lymph fluid takes as it passes through lymph nodes.

A

Circulation of lymph:
– 1. Afferent lymphatics
– 2. Subcapsular sinus
– 3. Trabecular and cortical sinuses
– 4. Medullary sinus
– 5. Efferent lymphatics
– 6. Other lymphocenters
– 7. Large lymph collecting ducts
– 8. Thoracic duct
– 9. Cranial vena cava, right atrium, subclavian vein

48
Q

Describe in detail (*as presented in class), the basic immune response to invading material such as bacteria.

A
  • Humoral (effective against extracellular pathogens e.g. neutralizing toxins, bacteria, viruses)
    – B cells respond directly to antigens
    – Activated B cells differentiate into plasma cells and memory cells
  • Plasma cells
    – Produce antibodies to a specific Antigen (Ag)
    – Secrete antibodies (Abs) into medullary sinus
    – Antibodies move from medullary sinus to general circulation
    – *Die once Ag is neutralized
  • Memory cells
    – B cells and T cells capable of responding to a specific Ag
    – Move through circulation and lymph nodes
    – Become activated when the Ag is contacted
    – B cells differentiate into plasma cells
    – Long lived (years)
  • Cell mediated (effective against intracellular pathogens e.g. bacteria, fungi, viruses, tumor cells)
    – 1. Ag ingested by an antigen presenting cell (APC = macrophage, dendritic cell, or B cell).
    – 2. Ag is broken into fragments.
    – 3. Ag fragment is bound to an MHC (I or II) which is incorporated into the cell membrane (Ag protrudes from the cell surface).
    – 4. Binding of Ag with a T cell receptor (TCR) on a mature T cell elicits an immune response
  • MHC I response
  • MHC II response
  • Generalized Primary response
    – 1. Lymph flows: afferent lymphatics -> subcapsular sinus -> trabecular and paracortical sinuses -> medullary sinus -> efferent lymphatics
    – 2. Ag engulfed by macrophages and presented on cell surface
    – 3. Macrophages migrate to paracortex and activate specific T cells
    – 4. Activated T cells migrate to cortex and activate specific B cells (*cell contact between T helper and B cells are required for Ab production and clonal expansion of B cells)
    – 5. Activated B cells migrate to medulla and exit node via efferent lymphatics
49
Q

Describe the structure, location, and function of tonsils, Peyer’s patches, and other diffuse lymphatic tissue.

A

Tonsils
– Solitary or aggregated lymph nodules and diffuse mononuclear cells located within the pharyngeal mucosa
– Forms a ring of lymphatic tissue (Waldeyer’s ring) encircling the oropharynx (tonsil of soft palate; palatine and lingual tonsils) and incompletely encircling the nasopharynx (pharyngeal tonsil, tubal tonsil (*species dependent – at rostral edge of Eustachian tube)
– Follicular
* Tonsillar follicle – blind, branched (sometimes) evagination of surface epithelium (tonsillar crypt) surrounded by lymphatic tissue
* Examples: palatine tonsils (humans, horses, swine, ruminants); lingual tonsil (humans, horses, cattle); tubal tonsil (swine); paraepiglottic tonsil (sheep, goats, swine)
– Non-follicular
* Single layer of lymphatic tissue
* Bulges into lumen or folded to increase surface area
* Examples: palatine tonsil (carnivores); pharyngeal tonsils (all domestic animals); tubal tonsil (ruminants)
* MALT
– Dense, unencapsulated (e.g. Peyer’s patches)
* GALT (gut associated lymphatic tissue) of intestinal tract
* Aggregated lymph nodules within the mucosa of small intestine
* Bulge into lumen of intestine
* Overlaid with a few villi
* Secondary nodules
– Zone of mixed lymphocytes and macrophages immediately below epithelium
– Germinal center (proliferating and maturing B cells)
– Mantle zone (small lymphocytes)
– Area between follicles (T cells)

Histology (15 decks)

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